A senior police officer in Orissa state said 35 bodies had been recovered as New Delhi rushed federal commandos to bolster local security forces.
The crackdown, concentrated in the thickly forested districts of Ganjam, Kandhamal and Nayagarh, about 300 kilometres (186 miles) southwest of the state capital Bhubaneswar, came after 13 policemen and one civilian died in Maoist raids on security posts overnight Friday.
A senior police officer, who did not wish to be named, said the 35 bodies recovered Tuesday included those of 20 killed over the weekend. Three security personnel had also been killed, he added.
A federal home ministry official in New Delhi told AFP that 500 "special police" forces were sent to Orissa Monday.
"We understand that they have arrived in the state and will be joining the security operation there," said the source.
Armoured vehicles and "supplies including arms and ammunition have been sent to the area to ensure the operation is successful," he added.
On Monday, security personnel said they had recovered a huge quantity of weapons in the fighting.
Orissa is one of India's poorest states and part of an eastern swathe of the country where the Maoists, who say they are fighting for the rights of neglected tribal people and landless farmers, appear to be gaining ground.
The insurgency grew out of a peasant uprising in 1967 and has hit half of India's 29 states.